The invention concerns a device for determining the torque exercised on a shaft, wherein the shaft comprises a first shaft section and a second shaft section, wherein the two shaft sections can be rotated relative to each other, a multi-pole magnetic ring which surrounds the first shaft section and is connected thereto, and a stator holder which is mounted to the second shaft section, wherein two stator elements are mounted to the stator holder and each stator element has fingers which protrude in an axial or radial direction and which are distributed uniformly at least over part of the periphery and have gaps inbetween, wherein the fingers of each stator element are interconnected via a magnetic flux ring, the magnetic flux rings having a mutual separation, and a magnetic field sensor is disposed between the magnetic flux rings, wherein the magnetic field sensor is associated with at least one magnetic flux concentrator.
U.S. Pat. No. 4,984,474 discloses a torque sensor which is formed substantially from one or more magnetic rings and two stator elements which have a low number of poles. The low pole number has the disadvantage that the signal measured by the sensor is modulated with a waviness when the steering shaft rotates, which can be compensated for only by suitable electronic addition of two signals which are offset by half a pulse width or by flux collecting rings of a completely annular shape. The torque sensor of this design is also relatively sensitive and susceptible to disturbances, since the magnetic flux concentrator is mounted radially outside of the stators. Such a design is also highly susceptible to concentricity tolerances. Finally, the stators comprise spacers formed by separate rings which render the assembly relatively complex.
FR 2,821,668 A1 discloses a device wherein the sensor consists of a discretely formed multi-pole magnetic ring and two nested soft-magnetic stators. These stators have finger-shaped structures on the radial inner side which scan the magnetic poles, and an annular gap on the radial outer side accommodating a stationary magnetic field sensor.
Pole division must be relatively coarse through discrete design of the magnet wheel (pole width 20°) which produces a likewise large linearity range which is not completely utilized since the range of the angle to be measured is only approximately ±3° to 5° due to the required rigidity of the torsion system. The magnetic flux cannot be optimally utilized since the air gap forming the magnetic return is uniformly formed across the entire periphery such that the magnetic flux is distributed over a large surface and is therefore only relatively small at the location of the magnetic field sensor.
Although highly remanent magnets are used, this device shows little sensitivity, and the measuring signal depends greatly on mechanical tolerances such as the width of the air gap where the flux density is measured.
DE 102 22 118 A1 discloses designs with annular flux conductors or magnetic flux collecting rings which are disposed on the outer side of the stators or magnet yokes. The design of the flux conductors disadvantageously leads to great expense and not all influences of radial and axial tolerances of the stators can be compensated for.
Mechanical tolerances in production and assembly of the components conducting the magnetic flux, in particular the stators, cannot be prevented. In all conventional constructions, these tolerances may have a direct effect on the size of the air gaps located in the magnetic circle and therefore a disturbing effect on the measuring signal thereby reducing the accuracy or producing erroneous measurements.
It is therefore the underlying purpose of the invention to further develop a device of the above-mentioned type to reduce the effect of the tolerances on the measuring result.